This invention relates to an improved electro-magnetically controlled pet door. However, the term xe2x80x9cpet doorxe2x80x9d will be used hereafter and is intended to refer to an entrance designed for animals such as domestic cats or small dogs.
Pet doors are frequently fitted to houses to allow the pet to enter and leave of its own free will. A pet door of this type would typically have a door pivotally mounted in a frame, the door being of a size such that the pet can readily push it open with its nose or paw. The opened door is returned to its closed position by gravity or by means of a small spring to eliminate unwanted draughts after the animal has passed through.
One draw-back of pet doors of this type which concerns pet owners is that stray pets will often try to enter the house. In order to prevent this problem, xe2x80x9cselectivexe2x80x9d pet doors have been designed which ensure that the door into the house is locked by a latch which is rendered inoperative in response to an xe2x80x9coperatorxe2x80x9d carried by the pet.
Various prior art solutions have been proposed but none of them has been found to be particularly satisfactory. UK patent No. 1567001 uses a magnetic responder linked to a latch member that is attracted towards an operator made of soft iron or to a bar magnet attached to the pets collar. The principle draw-back of this arrangement is that the operator is heavy and highly magnetic (thus attracting unwanted metallic objects) and the latch member has a very high inertia and will therefore not always respond quickly enough to the magnet attached to the cat as it passes over the magnetic responder. Thus, the pet may not have deactivated the latch by the time it presses the door against the latch. This patent also proposes another design which uses an inductance loop extending around the opening in conjunction with a control circuit to detect change in inductance. However, the major problem with this design is the high cost of production and also it is possible that the system could be incorrectly triggered by a pet wearing a steel address-carrying barrel or even a buckle on a collar.
UK patent No. 1588673 discloses a design using a magnetically operable switch in conjunction with adjustable biasing means located directly opposite the switch. Although this design makes it possible to render a single reed switch sufficiently sensitive to allow for the deficiencies of using a single unbiased switch, in practice it demands relatively expensive circuitry to create a time delay and then energise a resetting coil positioned around the reed switch in order to reopen the reed switch, which could otherwise remain closed under the influence of the biasing magnet. A further problem with this arrangement is that the adjustable biasing needs adjustment in situ to compensate for local magnetic effects which can be awkward and is certainly an undesirable task for the pet owner to perform.
A further prior art proposal is disclosed in U.S. Pat No. 4022263 in which the problem of encouraging the pet to enter the door centrally and thus come into sufficient proximity to a single unbiased magnetically operable switch is achieved by mounting the switch on an external door taking the form of a flexible iris positioned in front of an interior swing door. This design is extremely expensive to manufacture largely as a result of its two door construction. A further disadvantage is that the unit is fairly bulky which makes it unsuitable for installation in a domestic door.
The Applicant improved upon the aforementioned prior art devices and developed the design disclosed in their UK patent No. 2.223.257. This provides an electromagnetically controlled pet door comprising a door pivotally mounted in a door aperture of a frame and an electrically controlled catch mechanism normally preventing opening of the door in at least one direction that is released when a magnet carried by an animal approaching the door is sensed by a sensor which comprises two or more reed switches on or in the frame connected electrically in parallel, the switches being disposed in an array extending circumferentially of said door aperture. Whilst this design represented a substantial improvement over the pet doors of the prior art referred to above, it was found that the pet door would not always work satisfactorily with larger animals because the magnet around their neck was further away from its nose used to open the door and it would therefore sometimes be out of the operating range of the reed switches. One way of solving is problem would be to increase the size of the magnet around the animals neck but this was not acceptable as the heavier magnet would then be uncomfortable for the animal to wear and would attract unwanted metallic objects.
It is an object of the present invention therefore to provide a pet door in which the sensitivity of the reed switches is increased without the need for increasing the size of the magnet around the animals neck.
According to the present invention there is provided an electro-magnetically controlled pet door comprising a door pivotally mounted in a door aperture in a frame, an electrically controlled catch mechanism normally preventing opening of the door in at least one direction that is released when the presence of a magnet carried by an animal approaching the door is sensed by a sensor comprising two or more reed switches on or in the frame connected electrically in parallel, said switches being disposed in an array extending circumferentially of said door aperture and having normally open contacts, the contacts of one or more of the switches closing in the presence of a magnet carried by an animal, wherein the pet door also includes magnetic field producing biasing means operable to increase the sensitivity of the reed switches to an animal borne magnet, said magnetic field producing biasing means comprises first and second magnets located beyond respective ends of the sensor and displaced transversely therefrom so as to produce a flux path extending along said sensor between the pole of the first magnet and the pole of the other magnet facing the sensor so that the contacts automatically open again when the presence of the magnet carried by the animal is no longer sensed by the reed switches.
According to a further aspect of the invention, there is provided an electro-magnetically controlled pet door comprising a door frame with an aperture therein, a door pivotally mounted in said door aperture, a sensor comprising a plurality of parallel-connected reed switches having normally open contacts and arranged endto-end transversely of said frame such that at least one reed switch will close in the presence of a magnet carried by an animal approaching the door for passage therethrough, magnetic field producing biasing means for increasing the sensitivity of said sensor to an animal-borne magnet, and an electrically controlled catch mechanism normally preventing opening of the door in at least one direction and released by the closing of any of said reed switches, wherein the biasing means comprises first and second magnets located beyond respective ends of the sensor and displaced transversely therefrom so as to produce a flux path extending along said sensor between the pole of the first magnet and the pole of the other magnet facing the sensor.
Preferably the magnetic biasing means comprise a pair of magnets each positioned closely adjacent one of said reed switches., the ends of the magnets facing the reed switches being of opposite polarity.
Alternatively, the sensor can comprise three reed switches which are generally axially aligned to provide a central reed switch between two end switches, the magnetic biasing means comprising a pair of magnets each of which is positioned closely adjacent one of said end switches, the ends of the magnets facing the reed switches being of opposite polarity.
Preferably the reed switches are disposed in the frame coaxially with their common axis parallel with the plane of said aperture and spaced therefrom oppositely to said one direction, the main axis of the biasing magnets being at 9xc2x0 to the common axis of the reed switches.
In the preferred embodiment, the reed switches are positioned in an outward extension of the lower surface of the frame in which the door pivots.
In the preferred embodiment, the reed switches are mounted on a platform which forms part of a chassis on which the catch mechanism is mounted, said platform extending within said outward extension of the lower surface of the frame in which the door pivots. Conveniently the reed switches are mounted at the front of said platform and they are axially aligned.